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Dive into the research topics where Mario Estévez is active.

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Featured researches published by Mario Estévez.


Canadian Journal of Neurological Sciences | 2011

Autonomic, EEG, and behavioral arousal signs in a PVS case after Zolpidem intake.

Calixto Machado; Mario Estévez; Jesús Pérez-Nellar; Joel Gutierrez; Rafael Rodríguez; Maylén Carballo; Mauricio Chinchilla; Liana Portela; Maria C. Garcia-Roca; Carlos Beltrán

the paradoxical “arousing” effect of Zolpidem, a highly selective nonbenzodiazepine gamma aminobutyric acid (GABA) agonist acting on the [omega]-1 site of the GABA A receptor, in persistent vegetative state (PVS), in minimally conscious state (MCS) patients, ischemic stroke cases, after brain injury, and in patients suffering hypoxic encephalopathy.1 We describe here this paradoxical arousing effect in a PVS case assessing autonomic, electroencephalographic (EEG), and behavioral changes, after Zolpidem uptake. This case report is the first to show the importance of using heart rate variability (HRV) methodology and EEG to assess autonomic and brain functional changes in a PVS case, during this pharmacological intervention.


Journal of Autism and Developmental Disorders | 2015

QEEG Spectral and Coherence Assessment of Autistic Children in Three Different Experimental Conditions

Calixto Machado; Mario Estévez; Gerry Leisman; Robert Melillo; Rafael Rodríguez; Phillip DeFina; Adrián Hernández; Jesús Pérez-Nellar; Rolando Naranjo; Mauricio Chinchilla; Nicolás Garófalo; José Vargas; Carlos Beltrán

We studied autistics by quantitative EEG spectral and coherence analysis during three experimental conditions: basal, watching a cartoon with audio (V–A), and with muted audio band (VwA). Significant reductions were found for the absolute power spectral density (PSD) in the central region for delta and theta, and in the posterior region for sigma and beta bands, lateralized to the right hemisphere. When comparing VwA versus the V–A in the midline regions, we found significant decrements of absolute PSD for delta, theta and alpha, and increments for the beta and gamma bands. In autistics, VwA versus V–A tended to show lower coherence values in the right hemisphere. An impairment of visual and auditory sensory integration in autistics might explain our results.


International Journal on Disability and Human Development | 2016

Spectral analysis of heart rate variability

Mario Estévez; Calixto Machado; Gerry Leisman; Talía Estévez-Hernández; Asdrúbal Arias-Morales; Julio Montes-Brown

Abstract Spectral analysis (SA) has been extensively applied to the assessment of heart rate variability. Traditional methods require the transformation of the original non-uniformly spaced electrocardiogram RR interval series into regularly spaced ones using interpolation or other approaches. The Lomb-Scargle (L-S) method uses the raw original RR series, avoiding different artifacts introduced by traditional SA methods, but it has been scarcely used in clinical settings. An RR series was recorded from 120 healthy participants (17–25 years) of both genders during a resting condition using four SA methods, including the Classic modified periodogram, the Welch procedure, the autoregressive Burg method and the L-S method. The efficient implementation of the L-S algorithm with the added possibility of the application of a set of options for the RR series pre-processing developed by Eleuteri et al., and also the results obtained in this study, show that the L-S method can be a good choice for future clinical studies. The L-S method seems particularly useful when the heart rates of studied participants will be below 60 or over 120 beats per minute. Nevertheless, it is important to the development of a smoothing procedure for the L-S spectra to avoid the picky behavior of the L-S power spectrum. The implementation of the L-S algorithm used in this study has been recently published by other authors included in our references, and brings some particular filtering features. The results obtained, comparing the four spectral methods, show that this implementation seems particularly useful when the heart rates of studied participants will be below 60 or over 120 beats per minute. Nevertheless, it is important to recommend for all existing L-S software implementations, the development of a smoothing procedure to avoid the picky behavior of the L-S power spectrum.


Clinical Neurophysiology | 2013

Heart rate variability for assessing comatose patients with different Glasgow Coma Scale scores

Yazmina Machado-Ferrer; Mario Estévez; Calixto Machado; Adrián Hernández-Cruz; Frederick R. Carrick; Gerry Leisman; Robert Melillo; Phillip DeFina; Mauricio Chinchilla; Yanín Machado

OBJECTIVE To assess the autonomic nervous system (ANS) in coma by heart rate variability (HRV). METHODS Sixteen comatose patients and 22 normal subjects with comparable ages and genders were studied. Patients were classified in two subgroups according to the Glasgow Coma Scale (GCS). Time, frequency, and informational HRV domain indices were calculated. RESULTS A notable reduction of HRV was found in patients. Regarding the time domain indices, the triangular index, and the Delta_RRs, were significantly reduced in the subgroup with GCS=3. Absolute power for the whole frequency spectrum decreased whenever GCS scores were lower. A significant decrement was found for absolute power of the VLF and LF bands in the subgroup of GCS=3, and although it was lower for the HF band in these patients, those changes were not statistically significantly different. The LF/HF ratio and the Shannon´s entropy indices were significantly reduced in the subgroup with GCS=3. Our results are discussed regarding the progressive dysfunction the ANS networks when coma deepens. CONCLUSIONS The HRV procedure is a powerful tool to assess the ANS in comatose patients. SIGNIFICANCE HRV is a minimally invasive, low-cost methodology, suitable for assessing the ANS in coma.


Brain Injury | 2013

Zolpidem induces paradoxical metabolic and vascular changes in a patient with PVS

Rafael Rodriguez-Rojas; Calixto Machado; Lázaro Álvarez; Maylen Carballo; Mario Estévez; Jesús Pérez-Nellar; Nancy Pavón; Mauricio Chinchilla; Frederick R. Carrick; Philip DeFina

Abstract Introduction: Zolpidem is a non-benzodiazepine drug used for the therapy of insomnia, which has selectivity for stimulating the effect of GABA-A receptors. Recently, a paradoxical arousing effect of zolpidem in patients with severe brain damage has been repeatedly reported. Methods: A placebo-controlled magnetic resonance study was conducted to evaluate its effect on BOLD and metabolites spectral signals in a patient with severe brain injuries and an age-matched healthy volunteer. A multi-modal analysis was used to assess aspects in the pharmacologically-induced changes in the resting-state brain metabolism. Results: A significantly increased BOLD signal was transiently localized in the left frontal cortices, bilateral anterior cingulated areas, left thalamus and right head of the caudate nucleus. The healthy subject showed a deactivation of the frontal, parietal and temporal cortices. BOLD signal changes were found to significantly correlate with concentrations of extravascular metabolites in the left frontal cortex. It is discussed that, when zolpidem attaches to modified GABA receptors of neurodormant brain cells, brain activation is induced. This might explain the significant correlations of BOLD signal changes and proton-MRS metabolites in this patient after zolpidem. Conclusion: It was concluded that proton-MRS and BOLD signal assessment could be used to study zolpidem-induced metabolic modulation in a resting state.


International Journal on Disability and Human Development | 2010

Heart rate variability changes induced by auditory stimulation in persistent vegetative state

Joel Gutierrez; Calixto Machado; Mario Estévez; Ana Olivares; Héctor Hernández; Jesus Perez; Carlos Beltrán; Gerry Leisman

Abstract Previous studies, using neuroimaging and electrophysiology, have identified the presence of cerebral responses to auditory stimulation in clinically unresponsive persistent vegetative state (PVS) patients. In normal individuals, it has been shown that stimulation with emotional content has a strong influence on autonomic cardiovascular regulation tested by heart rate variability (HRV). In this paper, we assessed responses to auditory stimulation with emotional content in PVS and minimally conscious (MCS) cases by HRV. We found a pattern of changes induced by auditory stimulation in three of our patients (decreased heart rate, increased HRV, decrease power in the low and increased power in high frequencies) consistent with increased cardiovagal stimulation. Both time and frequency domain changes were more pronounced during affective than during non-affective auditory stimulation, suggesting that PVS patients are able to discriminate between stimuli of different content and are more reactive to emotional than non-emotional stimulation. Our results demonstrate (is a conclusion, should be in present) that auditory stimulation can induce recordable changes in HRV in some PVS cases, providing evidence that these patients retain some preserved cognitive function examined by cardiovascular correlates. The use of HRV to study residual cognitive functions could have practical implications for the management of PVS and MCS.


Brain | 2015

Anatomic and Functional Connectivity Relationship in Autistic Children During Three Different Experimental Conditions.

Calixto Machado; Rafael Rodríguez; Mario Estévez; Gerry Leisman; Robert Melillo; Mauricio Chinchilla; Liana Portela

A group of 21 autistic children were studied for determining the relationship between the anatomic (AC) versus functional (FC) connectivity, considering short-range and long-range brain networks. AC was assessed by the DW-MRI technique and FC by EEG coherence calculation, in three experimental conditions: basal, watching a popular cartoon with audio (V-A), and with muted audio track (VwA). For short-range connections, basal records, statistical significant correlations were found for all EEG bands in the left hemisphere, but no significant correlations were found for fast EEG frequencies in the right hemisphere. For the V-A condition, significant correlations were mainly diminished for the left hemisphere; for the right hemisphere, no significant correlations were found for the fast EEG frequency bands. For the VwA condition, significant correlations for the rapid EEG frequencies mainly disappeared for the right hemisphere. For long-range connections, basal records showed similar correlations for both hemispheres. For the right hemisphere, significant correlations incremented to all EEG bands for the V-A condition, but these significant correlations disappeared for the fast EEG frequencies in the VwA condition. It appears that in a resting-state condition, AC is better associated with functional connectivity for short-range connections in the left hemisphere. The V-A experimental condition enriches the AC and FC association for long-range connections in the right hemisphere. This might be related to an effective connectivity improvement due to full video stimulation (visual and auditory). An impaired audiovisual interaction in the right hemisphere might explain why significant correlations disappeared for the fast EEG frequencies in the VwA experimental condition.


Clinical Neurophysiology | 2012

qEEG may increase the reliability of diagnostic and prognostic procedures in cerebral arterial gas embolism.

Calixto Machado; Mario Estévez; Frederick R. Carrick; Robert Mellilo; Gerry Leisman

In this issue of Clinical Neurophysiology, Weenink et al. (this issue) present very interesting results about using quantitative electroencephalography (qEEG) in a swine model of cerebral arterial gas embolism (CAGE). CAGE is a severe complication which is known to occur during neurosurgical and cardiothoracic surgery as well as during many other invasive diagnostic and therapeutic procedures, leading to coma, permanent neurological deficits, and even death (Gao et al., 2009; Wheen and Williams, 2009; Rivalland et al., 2010; van Hulst et al., 2003; Lippmann et al., 2011). It is also an unfortunate hazard in scuba diving resulting in 18% of diving fatalities (Vann et al., 2005). Although gas bubbles can reach any organ, occlusion of the cerebral circulation is particularly deleterious because the nervous system is highly vulnerable to hypoxia (Visser et al., 2001; Jordan, 2004; Machado et al., 2004). CAGE is a serious hazard: when bubbles occlude the brain vasculature, intracranial pressure (ICP) increases and an extremely inhomogeneous distribution of blood flow in the brain may cause transient multifocal ischemia, and immediate disruption of the blood–brain barrier (van Hulst et al., 2003; Lippmann et al., 2011). According to van Hulst et al. (2003), the bubble first interacts with the blood leading to coagulation and complement activation, and a decrement of thrombocytes, secondly there is a reaction with the endothelium irritating the vascular wall leading to an instantaneous breakdown of the blood–brain barrier with vasogenic edema; finally the obstruction leads to distal hypoxia and ischemia resulting in neuronal cell death and cytotoxic edema. Of course, these pathophysiologic mechanisms lead to sudden and profound changes in cerebral metabolism and brain bioelectrical activity (van Hulst et al., 2003; Denoble et al., 2008; Lippmann et al., 2011). These are the basis to understand the interesting results of Weenink et al. (2012), using qEEG in a swine model of CAGE. These authors highlighted the following results:


Clinical Neurophysiology | 2012

Bilateral N20 absence in post-anoxic coma: Do you pay attention?

Calixto Machado; Mario Estévez; Rafael Rodríguez; Frederick R. Carrick; Robert Melillo; Gerry Leisman

In this issue of Clinical Neurophysiology, Van Putten presents an interesting simple biophysical model to explain the lack of correlation between EEG rhythms and the preservation of the N20 component of the somatosensory evoked potential (SSEP) in comatose patients after cardiac arrest. The author argues that EEG and SSEPs may reveal two distinctive functions of cortical neurons: input processing, supported by thalamocortical input, launching intracellular currents that trigger generation of cortical SSEP components, and output signals, processed by the synaptic mechanisms involved in EEG generation, where this latter process is seemingly more sensitive to hypoxia (Van Putten, 2012). The SSEP is a relatively simple, non-invasive, and inexpensive bedside technique for assessing the integrity of transmission within the central nervous system, and is commonly used to assess both brainstem and cortical function (Aguilar et al., 2011; Cruccu et al., 2008; Ma et al., 2011; Lenz et al., 2011; Schorl, 2008; Zanatta et al., 2011). While, clinical examination and EEG may be hampered by barbiturate therapy in patients with severe intracranial hypertension or by other forms of drug intoxication, hypothermia, and other metabolic disturbances, SSEP components are robust in these conditions (Machado, 1993, 2007; Buchner et al., 1988; Facco and Machado, 2004; Machado et al., 1993; Markand et al., 1990; Sala et al., 2007; Westeren-Punnonen et al., 2008). In this paper Van Putten reports a patient treated with moderate hypothermia and sedated with a low dosage of propofol (200 mg/h), who had no significant EEG activity, but preserved SSEP cortical responses. Therefore, SSEP is a reliable and an advantageous tool in the intensive care environment (Bouwes et al., 2009; Facco and Machado, 2004; Machado and Shewmon, 2004; Machado, 1993; Machado et al., 1993; Oddo and Rossetti, 2011; Zanatta et al., 2011). Several authors have shown that absence of the median nerve N20 response in comatose patients after a cardiac arrest, not treated with hypothermia, is consistently associated with for a poor outcome, if SSEPs are recorded within the first 24 h after brain insult (Bouwes et al., 2009; Cruccu et al., 2008; de Tourtchaninoff et al., 1999; Guérit, 1986, 1999, 2000, 2005, 2010; Rothstein, 2004, 2009, 2010; Zhang et al., 2011). As suggested by Van Putten, some controversies have appeared with mild therapeutic hypothermia (TH), because reports of single cases have suggested that a small percentage of patients may have a favorable clinical outcome, in spite of bilaterally absent N20 responses (Bouwes et al., 2009; Leithner et al., 2010). Rothstein (2010) and Leithner et al. (2010) differ on this issue. Leithner et al. reported that one of a series of 36 patients with bilaterally absent N20 components at day 3 after cardiac arrest, recovered consciousness and normal cognitive function, while the remaining 35 patients died without awakening or developed a persistent vegetative state. These authors concluded that bilateral absence of N20 as an outcome predictor needs to be re-evaluated, and not used in the decision to discontinue therapy. Rothstein (2010) pointed out that the single case reported by Leithner et al. was a 43-year-old male alcoholic who developed pneumonia and sepsis, and had asystole for 10 min. SSEP testing was not repeated until 18 months later, and N20 responses were then intact, and he suggested technical factors may have interfered with the SSEP recording. Leithner et al. denied any technical issues, and suggested that caution is reasonable when comparing prognostic parameters in non-hypothermia patients and hypothermia patients (Rothstein, 2010). With this background Van Putten explains the discrepancy between EEG and SSEPs, as seen in data from patients in post-anoxic coma after cardiac arrest treated with TH by proposing a simple biophysical model based on SSEP and EEG generation (Van Putten, this issue). The origin of the N20 component of the SSEP has been extensively discussed in literature (Baumgartner et al., 2010; Daubin et al., 2008; Facco et al., 2002; Gobbele et al., 2003, 2004; Machado, 1993, 2007; Machado and Shewmon, 2004; Machado et al., 1993; Murakami et al., 2008; Shimazu et al., 2000; Sonoo et al., 1999; Wagner et al., 1993). Chiappa (1983) proposed that N20 might not reflect cortical activity but instead the negative counterpart of an approach positivity of white-matter impulses entering the somatosensory cortex. Nonetheless, recent reports indicate that N20 is generated in the somatosensory cortex, in the layers III–IV and V of area 3b (Allison et al., 1991, 1992; McCarthy et al., 1991; Baumgartner et al., 2010; Jaramillo et al., 2008; Ikeda et al., 2002, 2005; Samaniego et al., 2011) and not in subcortical structures, as suggested by Chiappa (1983). Ikeda et al. (2005) have recently proposed that the N20 component was evoked by two dipolar current generators. One generator may have its initial extracellular current sink in the border between layers IV and V, but its sink progressively shifts toward layer II as N20 reaches its peak amplitude. The second generator has a sink in layer V, which is motionless unlike the narrower generator. This hypothesis implies that the median nerve N20 should be due to currents directed from a deep layer of the cortex to shallower layers. It has been advocated that SSEPs reflect thalamocortical (glutamatergic) synaptic function (Leithner et al., 2010). EEG generation has been a subject of research for neuroscientists over many decades. The interaction between the superficial and deep pyramidal cells may induce a recordable potential from the scalp, resulting in EEG. Sufficient synchronization of pyramidal cells is necessary for the generation of extracellular currents, based


Neurology | 2018

Reader response: An interdisciplinary response to contemporary concerns about brain death determination

Calixto Machado; Mario Estévez; Phillip DeFina; Gerry Leisman

We read with interest the Contemporary Issues by Lewis et al.1 Previously, Dr. Bernat defended the whole-brain concept of brain death (BD),2 and the US Presidents Commission recommended its adoption by all US states.3 In 2015, Wijdicks stated, “the irreversible absence of functions of the brainstem is the necessary and sufficient component of brain death.”4 This view fully pertains to brainstem death, and not to the whole-brain criterion.5 The American Academy of Neurology summit concluded that “BD is defined by irreversible loss of consciousness and brainstem function,” according to the whole-brain criterion.1

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Dive into the Mario Estévez's collaboration.

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Gerry Leisman

Universidad de Ciencias Medicas

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Mauricio Chinchilla

Hermanos Ameijeiras Hospital

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Robert Melillo

Leeds Beckett University

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Jesús Pérez-Nellar

Hermanos Ameijeiras Hospital

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Rafael Rodriguez-Rojas

International Centre for Theoretical Physics

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Yanín Machado

Hermanos Ameijeiras Hospital

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Alejandro Pando

Hermanos Ameijeiras Hospital

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Gerry Leisman

Universidad de Ciencias Medicas

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Rafael Rodriguez

University of Texas Medical Branch

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Adam Schiavi

Johns Hopkins University

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